Variable resistor



Oct. 10,1944. F RS v 2,359,757

VARIABLE RESISTOR Filed Aug. 20, 1940 I lame/vibe fi'/cof/ar 6/6/7478 MIPNCY Patented Oct. 10, 1944 VARIABLE RESISTOR Friedrich Gieffers, Berlin-Spandau, Germany;

vested in the Alien Property Custodian Application August 20, 1940, Serial No. 353,321 In Germany July 7, 1939 2 Claims.

The invention relates to variable resistance devices for electric circuits and, in particular, to devices of rheostat type in which the efiective resistance of a resistor is varied by means of a slide contact.

An object of the invention is to improve resistance devices of the above type by preventing the overloading of local points or elements of the resistance body and ensuring that the fiow of current through the resistor is not concentrated at substantially a single edge of the slide contact but is offered a number of substantially equivalent current paths.

In the copending application Serial No. 355,299, filed September 4, 1940, since become Patent No. 2,356,512, issued August 22, 1944, are illustrated and described variable resistors in which an undue crowding of the current paths at one edge of a. slidable contact is prevented. The present invention presents another possibility of preventing such a crowding of the current paths. According to the invention in subdividing the resistor in insulating layers or layers of high specific resistance, extending in the desired direction of the current paths.

The accompanying drawing illustrates diagrammatically some embodiments of the invention.

Fig. 1 shows a longitudinal section through a variable resistance device comprising a prismatic resistor and a slide contact;

Fig. 2 shows a front view of a device having a rotatable contact associated with two straight resistors, and

Fig. 3 shows a cross section of a resistance device comprising a rotatable contact associated with two arcuate resistors.

According to Fig. 1, a contact 3 consisting preferably also of resistance material slides over a resistor w. The contact is subdivided (laminated) perpendicularly to the contact surface and composed of insulating layers 1' and flat resistance members 1'. The resistance members 1' are connected by a common contact terminal I). The resistor w is provided at the side opposite to the contacts 3 with a contact terminal a. The distribution of the current paths extending within both bodies 8 and 1.0 between the terminals a and b is substantially uniform so that the contact edge is prevented from being too heavily loaded.

Fig. 2 shows an arrangement in which an approximately uniform distribution of the current paths is obtained by a symmetrical arrangement of two resistors. The two resistors wi 202 are bridged by a. laminated contact s1, preferably of good conductivity, lying crosswise with respect to the two bodies and rotatable about the axis 1.. The contact s1 is composed of contact members c1 separated from one another by insulating layers i1. When rotating the contact 31 in the direction of the arrow, for instance into the position indicated by broken lines, the ends of the contact are moved away from the current terminals a1 and 412 so that an increasing resistance is inserted in the circuit. Owing to the symmetrical arrangement, the various current paths extending within the contact have substantially the same length so that a concentration of the current in certain paths is prevented. The lamination of the contact supports a uniform current distribution in the resistors w and L02.

An improved arrangement of the above character is shown in Fig. 3. Two resistors ws and 204 of arcuate shape are arranged opposite each other and have a cylindrical contact surface in engagement with a. cylindrical contact structure. This structure contains contact members 02 separated from one another by insulating layers i2 and covered by cylindrical sections is and it also of insulating material. The contact terminals (1.3 and a; of the resistors w: and m; respectively are arranged on the outer cylindrical surface of the resistors and extend over a considerable portion of the arcuate length of the resistors. Each terminal a: and 114 forms an extension ds and d4, respectively, which covers one of the radial end faces of the resistance body and has a contact surface flush with the cylindrical contact surface of the body. Depending upon the position of the contact, the latter inserts in the circuit more or less resistance. In the position shown, the resistance device is practically Without resistance.

What is claimed is:

1. A variable resistance device, comprising two resistance bodies each having a slide surface, said bodies being arranged separate from each other and in a fixed relation to each other, each having a contact terminal for supplying current, a contact engaging said two resistance bodies and being movable relative to said bodies to vary the effective resistance of the total current path between said terminals, said contact being subdivided into a plurality of contact members insulated from each other and extending in the direction of the current flow through said contact between the engaged surfaces of said resistance bodies.

2. A variable resistance device, comprising two resistance bodies of arcuate shape having each a cylindrical contact surface arranged substantially opposite to the cylindrical contact surface of the other body, and a revolvable structure disposed between said bodies and in slidable engagement with said cylindrical surfaces, said structure com- 

